1. Field of Invention
The present invention relates to a system for calibrating a device, and more specifically, for calibrating a direction-finding system in a device using a wireless target tag.
2. Background
Modern society has quickly adopted, and become reliant upon, handheld devices for wireless communication. For example, cellular telephones continue to proliferate in the global marketplace due to technological improvements in both the quality of the communication and the functionality of the devices. These wireless communication devices (WCDs) have become commonplace for both personal and business use, allowing users to transmit and receive voice, text and graphical data from a multitude of geographic locations. The communication networks utilized by these devices span different frequencies and cover different transmission distances, each having strengths desirable for various applications.
Cellular networks facilitate WCD communication over large geographic areas. These network technologies have commonly been divided by generations, starting in the late 1970s to early 1980s with first generation (1G) analog cellular telephones that provided baseline voice communication, to modern digital cellular telephones. GSM is an example of a widely employed 2G digital cellular network communicating in the 900 MHz/1.8 GHz bands in Europe and at 850 MHz and 1.9 GHz in the United States. This network provides voice communication and also supports the transmission of textual data via the Short Messaging Service (SMS). SMS allows a WCD to transmit and receive text messages of up to 160 characters, while providing data transfer to packet networks, ISDN and POTS users at 9.6 Kbps. The Multimedia Messaging Service (MMS), an enhanced messaging system allowing for the transmission of sound, graphics and video files in addition to simple text, has also become available in certain devices. Soon emerging technologies such as Digital Video Broadcasting for Handheld Devices (DVB-H) will make streaming digital video, and other similar content, available via direct transmission to a WCD. While long-range communication networks like GSM are a well-accepted means for transmitting and receiving data, due to cost, traffic and legislative concerns, these networks may not be appropriate for all data applications.
Short-range wireless networks provide communication solutions that avoid some of the problems seen in large cellular networks. Bluetooth™ is an example of a short-range wireless technology quickly gaining acceptance in the marketplace. A 1 Mbps Bluetooth™ radio may transmit and receive data at a rate of 720 Kbps within a range of 10 meters, and may transmit up to 100 meters with additional power boosting. Enhanced data rate (EDR) technology also available may enable maximum asymmetric data rates of 1448 Kbps for a 2 Mbps connection and 2178 Kbps for a 3 Mbps connection. A user does not actively instigate a Bluetooth™ network. Instead, a plurality of devices within operating range of each other may automatically form a network group called a “piconet”. Any device may promote itself to the master of the piconet, allowing it to control data exchanges with up to seven “active” slaves and 255 “parked” slaves. Active slaves exchange data based on the clock timing of the master. Parked slaves monitor a beacon signal in order to stay synchronized with the master. These devices continually switch between various active communication and power saving modes in order to transmit data to other piconet members. In addition to Bluetooth™ other popular short-range wireless network technologies include WLAN (of which “Wi-Fi” local access points communicating in accordance with the IEEE 802.11 standard, is an example), Wireless USB (WUSB), Ultra Wideband (UWB), ZigBee (802.15.4, 802.15.4a), and UHF RFID. All of these wireless communication technologies have features and advantages that make them appropriate for various applications.
More recently, manufacturers have also begun to incorporate various resources for providing enhanced functionality in WCDs (e.g., components and software for performing close-proximity wireless information exchanges). Sensors and/or scanners may be used to read visual or electronic information into a device. A transaction may involve a user holding their WCD in proximity to a target, aiming their WCD at an object (e.g., to take a picture) or sweeping the device over a printed tag or document. Machine-readable technologies such as radio frequency identification (RFID), Infra-red (IR) communication, optical character recognition (OCR) and various other types of visual, electronic and magnetic scanning are used to quickly input desired information into the WCD without the need for manual entry by a user.
While substantial benefit may be realized in utilizing devices that include one or more of the features described above, these advantages may not be fully appreciated if the configuration required for utilizing these resources is burdensome. For example, a portable device may include some directional functionality (e.g., direction and/or position finding) that requires calibration. Antenna arrays and microphone arrays are examples of signal receiver array types usable in direction finding. These exemplary signal receiver arrays may receive signals that are processed in accordance with various algorithms to determine the direction towards the source of a target signal. In the exemplary case of a multi-antenna directional system, traditional calibration techniques would require each device to be placed in an anechoic chamber where the response to various signals may be measured using a network analyzer and an antenna positioner. Using this method, each device would have to be calibrated individually, making it prohibitive for use in a large-scale manufacturing process.
Further, even if calibration processes more suitable for manufacturing were to be devised, a device including a direction-finding system may require additional calibration post-manufacture. For example, devices may experience a variety of conditions on the way to an end consumer such as temperature extremes, impact, magnetic or electrical fields, etc. Further, even after a user begins to utilize a device, the performance characteristics of electronic components that support the directional system may change due to use, age, shock, temperature, exposure or simply due to malfunction. As a result, devices including a signal-based direction-finding system, even in normal use, may require occasionally recalibration.